The human visual system processes the available visual information both to recover the identity and use of objects, and to recover the three- dimensional (3D) structure or layout of the surrounding environment. In particular, the retinal projection of objects' motions in the environment-the optic flow-can be used to recover the 3D structure of those objects and their relationships to each other and the viewer. This ability to recover structure from motion (SFM) occurs both in humans and in various primate species. The specific aims of this proposal are to identify how certain components of optic flow, which are involved with the 3D layout of the environment, are processed within the human and macaque parietal cortex. Clinically, lesions of the posterior parietal cortex in humans produce a consistent and readily recognized set of symptoms which include deficits in visuo-spatial perception, loss of spatial memories, route-following defects, and oculomotor defects. All of these defects entail the disruption of spatial perception. There are also disruptions of the awareness of the body, the relation of body to the environment, and the perception of the topographic organization of the environment. These studies will assist in understanding the processes of motion perception through parietal cortex.